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VR4101

The VR4101 is a 64-bit microprocessor that implements the MIPS III ISA with MIPS16 ASE make by NEC however it does not implement the LL, LLD, SC and SCD instructions nor an FPU.

For application software Linux will emulate an FPU and the missing atomic load and store instructions so full compatibility with MIPS II and MIPS III software is provided. For best performance however applications may need to
be optimized.

The VR4101 consists of the low-power consumption VR4100; CPU core with cache memory, high-speed product-sum operation unit, and address management unit. It also has interface units for the peripheral circuits, such as DMA, software modem interface, serial interface, keyboard interface, IrDA interface, touch panel interface, real-time clock, A/D converter, and D/A converter required for the battery-driven portable information equipment. The external bus width of this device can be selected between 32 bits and 16 bits and supports external devices that require the performance level of a color LCD controller.

VR4102

The VR4102, which is a high-performance 64-/32-bit microprocessor employing the RISC (reduced instruction set computer) architecture developed by MIPS, is one of the RISC microprocessor VR-series products manufactured by NEC.

The VR4121 consists of the low-power consumption VR4100; CPU core with cache memory, high-speed product-sum operation unit, and address management unit. It also has interface units for the peripheral circuits, such as DMA, software modem interface, serial interface, keyboard interface, IrDA interface, touch panel interface, real-time clock, A/D converter, and D/A converter required for the battery-driven portable information equipment. The external bus width of this device can be selected between 32 bits and 16 bits and supports external devices that require the performance level of a color LCD controller.

This processor supports instruction set architecture (ISA) of MIPS I, MIPS II, MIPS III, and MIPS16. It does not support LL, LLD, SC, SCD, and floating point instructions.

Note that this processor does not incorporate a secondary cache, multi-processor processing function, or floating point arithmetic function.

VR4111

The VR4111, which is a high-performance 64-/32-bit microprocessor employing the RISC (reduced instruction set computer) architecture developed by MIPS, is one of the RISC microprocessor VR-series products manufactured by NEC.

The VR4121 consists of the ultra-low-power consumption VR4110; CPU core with cache memory, high-speed product-sum operation unit, and address management unit. It also has interface units for the peripheral circuits, such as DMA, software modem interface, serial interface, keyboard interface, IrDA interface, touch panel interface, real-time clock, A/D converter, and D/A converter required for the battery-driven portable information equipment. The external bus width of this device can be selected between 32 bits and 16 bits and supports external devices that require the performance level of a color LCD controller.

This processor supports instruction set architecture (ISA) of MIPS I, MIPS II, MIPS III, and MIPS16. It does not support LL, LLD, SC, SCD, and floating point instructions.

Note that this processor does not incorporate a secondary cache, multi-processor processing function, or floating point arithmetic function.

VR4121

The VR4121, which is a high-performance 64-/32-bit microprocessor employing the RISC (reduced instruction set computer) architecture developed by MIPS, is one of the RISC microprocessor VR-series products manufactured by NEC.

The VR4121 consists of the ultra-low-power consumption VR4120; CPU core with cache memory, high-speed product-sum operation unit, and address management unit. It also has interface units for the peripheral circuits, such as DMA, software modem interface, serial interface, keyboard interface, IrDA interface, touch panel interface, real-time clock, A/D converter, and D/A converter required for the battery-driven portable information equipment. The external bus width of this device can be selected between 32 bits and 16 bits and supports external devices that require the performance level of a color LCD controller.

This processor supports instruction set architecture (ISA) of MIPS I, MIPS II, MIPS III, and MIPS16. It does not support LL, LLD, SC, SCD, and floating point instructions.

Note that this processor does not incorporate a secondary cache, multi-processor processing function, or floating point arithmetic function.

VR4122

The VR4122 (µPD30122) is one of NEC Electronics VR Series RISC microprocessors and is a high-performance 64-/32-bit microprocessor employing the MIPS RISC architecture.

The VR4122 uses the high-performance, super power-saving VR4120 as the CPU core, and has many peripheral functions such as a DMA controller, serial interface, IrDA interface, and real-time clock. Configured with these functions, the VR4122 is suitable for high-speed battery-driven portable information systems. The external memory bus width can be selected from 32 bits and 16 bits, realizing high-speed data transfer.

VR4131

The VR4131, which is a high-performance 64-/32-bit microprocessor employing the RISC (reduced instruction set computer) architecture developed by MIPS, is one of the RISC microprocessor VR-series products manufactured by NEC Electronics.

The VR4131 incorporates the ultra low power consumption VR4130 CPU core provided with cache memory, a high-speed product-sum operation unit, and an address management unit. The VR4131 also has interface units for the peripheral circuits required for battery-driven portable information equipment, such as a DMA interface, a serial interface, an IrDA interface, a real-time clock interface, an interface for memories such as synchronous DRAM and page ROM, an NS16550-compatible serial interface, and a 3-wire clocked serial interface. This processor has an external memory bus width selectable from 16 or 32 bits and supports the PCI bus interface conforming to rev 2.1 as
the interface for an external device that requires the performance level of a color LCD controller.

The VR4131 is a MIPS III processor with and MIPS16 extension. However, it does not support the LL, LLD, SC, SCD, and is FPU-less.

Note that this processor does not incorporate a secondary cache, multi-processor processing function, or floating point arithmetic function.

VR4133

The VR4133 is a 200Mhz processor with 16kB of Primary Instruction cache and 16kB of D-cache. It has 32 TLB entries. The primary data cache line size is 32 bytes and the primary instruction cache line size is 32 bytes. Currently, this processor is fully supported in Linux versions 2.4 and 2.6.

TLB differences

The VR4100 TLB was optimized to support rather small systems. For this reason support for 1KB pages was added. Linux however does not support 1K pages — neither for MIPS nor any other architecture. At the same time NEC only implemented support for page sizes up to 256KB. This page size however is too small for Linux Huge Page support. As such hugetlbfs and Transparent Huge Pages are not available on the NEC VR41xx family.

The limited number of TLB entries as well typically small memory size of VR41xx-based systems makes neither feature appear very useful. However there are possible workarounds:

Pretend to Linux that the memory management huge page size is larger than the size supported at TLB level. The TLB exception handler would then only load a pair of 256K entries into the TLB. Of all alternatives in this list, this is the easiest to implement.

Emulate larger pages by loading several smaller TLB entries into the TLB